Just recently, I heard a speaker use a saying I've heard attributed to Lee Iaccoca, the former chairman of Chrysler: "No one on their death bed says, 'I wish I'd spent more time at the office.'" But, the speaker said it without attribution. Not even, "Someone once said..."
But beyond just doing the right thing, quoting someone also boosts your own credibility. It shows that you've done some research and looked into what others have said about your subject.
Conversely, failing to properly identify the source of a quote erodes your credibility. With so much available online today, chances are that people in your audience will know when you say something someone else has already said.
You wouldn't want someone to quote you without giving you credit. Don't abuse someone else's ideas.
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